A plant is heterozygous at a locus when its two alleles differ, for example Aa. Half its gametes carry A and half carry a. When heterozygous plants are crossed or selfed, their offspring segregate into different genotypes, which is why seed from a heterozygous plant varies.
In practice
Most cannabis cultivars on the market are highly heterozygous: they are hybrids of hybrids. That is why a seed pack from two famous parents throws a spread of plants and why an elite clone's seed rarely reproduces the clone. The clone holds its heterozygous combination intact only because it is propagated vegetatively.
"Het" is breeder shorthand for a plant known to carry one copy of a recessive allele, as in "het for the auto trait". A test cross or a DNA marker can confirm it.
Heterozygosity is not a defect. High heterozygosity in F1 hybrids is associated with hybrid vigour, and wild or landrace populations keep plenty of it.
Don't confuse with
- Homozygous: two identical alleles.
- Hybrid: a cross between different parents; hybrids are usually heterozygous at many loci, but a hybrid between two different inbred lines is uniform even so.
- Unstable: heterozygous plants are genetically normal; "unstable" in breeder talk means the seed line does not breed true.
An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different.A hybrid is the offspring of two genetically different parents; almost all modern cannabis is hybrid, built from crosses between landrace-derived and other lines.An elite cut is a famous, proven clone-only plant, often held by a few growers and traded rather than sold openly.A recessive allele only shows its effect when a plant carries two copies of it; in a single copy it is masked by a dominant allele and carried silently.F1 is the first generation of offspring from crossing two parents; if the parents are inbred and different, F1 plants are uniform and often show hybrid vigour.Heterosis (hybrid vigour) is the tendency of offspring from genetically different parents to outgrow or outperform both parents in traits such as vigour and yield.A landrace is a traditional, locally adapted cannabis population kept by farmers in one region over many generations, with its own type and plenty of internal variation.Inbreeding is mating between related plants, which raises homozygosity; an inbred line is the resulting population, measured by the inbreeding coefficient F.A plant is homozygous at a locus when it carries two identical alleles there (AA or aa), so it passes the same allele to every offspring.Segregation is the separation of a plant's two alleles at each locus into different gametes, so offspring of a heterozygous parent vary in which allele they get.
